ConstantExpression.cs source code in C# .NET

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                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / Core / Microsoft / Scripting / Ast / ConstantExpression.cs / 1305376 / ConstantExpression.cs
                        

                        
                            /* **************************************************************************** 
 *
 * Copyright (c) Microsoft Corporation.
 *
 * This source code is subject to terms and conditions of the Microsoft Public License. A 
 * copy of the license can be found in the License.html file at the root of this distribution. If
 * you cannot locate the  Microsoft Public License, please send an email to 
 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound 
 * by the terms of the Microsoft Public License.
 * 
 * You must not remove this notice, or any other, from this software.
 *
 *
 * ***************************************************************************/ 

using System.Diagnostics; 
using System.Dynamic.Utils; 

#if SILVERLIGHT 
using System.Core;
#endif

namespace System.Linq.Expressions { 

    ///  
    /// Represents an expression that has a constant value. 
    /// 
#if !SILVERLIGHT 
    [DebuggerTypeProxy(typeof(Expression.ConstantExpressionProxy))]
#endif
    public class ConstantExpression : Expression {
        // Possible optimization: we could have a Constant subclass that 
        // stores the unboxed value.
        private readonly object _value; 
 
        internal ConstantExpression(object value) {
            _value = value; 
        }

        internal static ConstantExpression Make(object value, Type type) {
            if ((value == null && type == typeof(object)) || (value != null && value.GetType() == type)) { 
                return new ConstantExpression(value);
            } else { 
                return new TypedConstantExpression(value, type); 
            }
        } 

        /// 
        /// Gets the static type of the expression that this  represents.
        ///  
        /// The  that represents the static type of the expression.
        public override Type Type { 
            get { 
                if (_value == null) {
                    return typeof(object); 
                }
                return _value.GetType();
            }
        } 

        ///  
        /// Returns the node type of this Expression. Extension nodes should return 
        /// ExpressionType.Extension when overriding this method.
        ///  
        /// The  of the expression.
        public sealed override ExpressionType NodeType {
            get { return ExpressionType.Constant; }
        } 
        /// 
        /// Gets the value of the constant expression. 
        ///  
        public object Value {
            get { return _value; } 
        }

        /// 
        /// Dispatches to the specific visit method for this node type. 
        /// 
        protected internal override Expression Accept(ExpressionVisitor visitor) { 
            return visitor.VisitConstant(this); 
        }
    } 

    internal class TypedConstantExpression : ConstantExpression {
        private readonly Type _type;
 
        internal TypedConstantExpression(object value, Type type)
            : base(value) { 
            _type = type; 
        }
 
        public sealed override Type Type {
            get { return _type; }
        }
    } 

    public partial class Expression { 
        ///  
        /// Creates a  that has the  property set to the specified value. .
        ///  
        /// An  to set the  property equal to.
        /// 
        /// A  that has the  property equal to
        ///  and the  property set to the specified value. 
        /// 
        public static ConstantExpression Constant(object value) { 
            return ConstantExpression.Make(value, value == null ? typeof(object) : value.GetType()); 
        }
 

        /// 
        /// Creates a  that has the 
        /// and  properties set to the specified values. . 
        /// 
        /// An  to set the  property equal to. 
        /// A  to set the  property equal to. 
        /// 
        /// A  that has the  property equal to 
        ///  and the  and
        ///  properties set to the specified values.
        /// 
        public static ConstantExpression Constant(object value, Type type) { 
            ContractUtils.RequiresNotNull(type, "type");
            if (value == null && type.IsValueType && !TypeUtils.IsNullableType(type)) { 
                throw Error.ArgumentTypesMustMatch(); 
            }
            if (value != null && !type.IsAssignableFrom(value.GetType())) { 
                throw Error.ArgumentTypesMustMatch();
            }
            return ConstantExpression.Make(value, type);
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.

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